Magnetron Sputtering Device In which Two Modes Of Magnetic Flux Distribution (Balanced Mode/Unbalanced Mode) Can Be Switched From One To The Other And Vice Versa, A Film Formation Method For Forming A Film From An Inorganic Film Formation Material Using The Device, And A Dual Mode Magnetron Sputtering Device And Film Formation Method For Forming A Film From An Inorganic Film Formation Material At A Low Temperature Using The Device

ABSTRACT

The first object of this invention is to provide a magnetron sputtering device in which switching the magnetic field arrangement from the balanced mode to the unbalanced one and vice versa can be easily achieved. The second object is to provide a dual magnetron sputtering device which allows one to rapidly form a film from an inorganic film formation material over a wide temperature range from a low to high temperature. Provided is a magnetron sputtering device in which a sputtering cathode is arranged to produce a balanced distribution of magnetic fluxes and in which an article that exhibits ferromagnetism at room temperature is removably placed close to the surface of the sputtering cathode for holding a material target such that conversion of the balanced magnetic field arrangement into the unbalanced one can be easily achieved by removing the ferromagnetic article. Further provided is a dual magnetron sputtering device in which an angle formed between two lines one extending from the surface of material target of one magnetron and the other from the surface of opposite target of the other magnetron falls within a range of 160 to 20°, preferably 160 to 70°, so that an active focus of plasma can converge onto a substrate, to enable the rapid formation of a film there at a low temperature. The rapid and low temperature film formation is further enhanced by adjusting the two magnetrons so as to produce an unbalanced distribution of magnetic fluxes, and using a gas mixture comprising two or more rare gases as a sputtering gas.

SPECIFICATION

A magnetron sputtering device in which the two modes of magnetic fluxdistribution (balanced mode/unbalanced mode) can be switched from one tothe other and vice versa, a film formation method for forming a filmfrom an inorganic film formation material using the device, and a dualmode magnetron sputtering device and film formation method for forming afilm from an inorganic film formation material at a low temperatureusing the device

TECHNICAL FIELD

In one aspect, the present invention relates to a magnetron sputteringdevice in which configuration of the magnetron cathode can be readilyaltered by switching to convert a balanced distribution of magneticfluxes into an unbalanced distribution of magnetic fluxes, and to a filmformation method for forming a film from an inorganic film formationmaterial using the device which has been set to produce an unbalanceddistribution of magnetic fluxes (this aspect of the invention will becalled “the first aspect of the invention” hereinafter).

In another aspect, the present invention relates to a dual modemagnetron sputtering device enabling the high speed formation of a filmat a low temperature, and to a sputtering method enabling the formationof a film at a low temperature using the aforementioned device (thisaspect of the invention will be called “the second aspect of theinvention” hereinafter).

BACKGROUND ART

With regard to a sputtering-based film formation device incorporating amagnetron, it has been known that configuration of the cathode of amagnetron can be classified to the balanced type and unbalanced one interms of the distribution of magnetic fluxes.

According to the balanced type magnetic flux designing, a magnetic fieldis produced so as to restrict plasma strictly locally to the surface ofa target which is placed on the surface of a cathode. To achieve thismode of magnetic field setting, a magnetron includes a plurality ofpermanent magnets, and adjusts the intensities of individual magnetssuch that magnetic fluxes emanating from N poles of the magnets passthrough a space adjacent to the target and converge almost totally to Spoles of the magnets, namely, a closed magnetic flux circuit is formedthrough the space. According to this mode of operation, it is possibleto restrict plasma strictly close to the surface of the target.

In contrast with this, according to the unbalanced type magnetic fluxdesigning, a magnetron includes a plurality of permanent magnets, andadjust the intensities of individual magnets such that one part ofmagnetic fluxes forms a closed circuit as does a magnetron preparedaccording to the balanced type magnetic flux designing, while the otherpart is radiated in a three-dimensional space to be dispersed diffusely(see URL: http://www.kobelco.co.jp/p109/pvd/ubms.htm).

These two types of magnetic flux designing have their own advantages anddisadvantages in terms of film formation. According to the balanced typedesigning, it is possible to restrict plasma necessary for filmformation strictly close to the surface of cathode which allows the highspeed formation of a film.

In contrast, the cathode of a magnetron sputtering device arranged toproduce a magnetic field evoking an unbalanced distribution of magneticfluxes allows plasma not only to be distributed close to the surface ofcathode but also to be dispersed diffusely towards the surface of asubstrate which is placed opposite to the cathode and upon which a filmis to be formed, which allows the more vigorous spread of ions andradicals or reactive elementary particles in plasma onto the surface ofthe substrate than is possible with a corresponding cathode arrangedaccording to the balanced type designing, thereby achieving the moreenhanced elicitation of reactions and growth of crystals upon thesurface of the substrate, although the cathode in question does notallow the formation of a film to proceed as fast as the comparablecathode based on the balanced type designing.

Thanks to the above merits, so it has been thought, the cathode of amagnetron sputtering device arranged to produce an unbalanced magneticfield can be applied to a substrate constituted of a heat-labilematerial which will reject a film formation process necessarilyaccompanied by high temperature, and will allow a well-crystallized filmto be formed at a lower temperature than is possible with a comparablecathode prepared according to the balanced type magnetic flux designing.

When a film is to be formed on a substrate, the most appropriate mode ofmagnetic flux arrangement should be chosen according to a given purposeof the film formation. To meet such a requirement, it is ideal toprepare two devices one operating exclusively according to the balancedtype magnetic flux designing and the other to the unbalancedcounterpart, and to choose either one according to a given requirementof film formation. However, the sputtering device is so expensive thatthe problem under study is generally solved by removing the cathode of asingle existing device and adjusting parameters of the cathode so thatit allows the generation of magnetic fluxes whose distribution is mostappropriate for a given purpose of film formation, that is, the magneticflux distribution is changed from one mode to the other or vice versaaccording to a given purpose of film formation.

This switching operation will be described below with reference toattached drawings taking, as an example, a case where the cathode of amagnetron sputtering device which has been set to the balanced mode isaltered to give a magnetic field to evoke an unbalanced distribution ofmagnetic fluxes. Needless to say, the reverse case may happen as often.

Referring to FIG. 1, magnetic fluxes (not shown) for restricting plasma(not shown) to the surface of a material target (4) are generated by amagnet assembly (8) comprising a plurality of permanent magnets (7)placed behind a backing plate (5) which holds the material target (4).The magnetic fluxes pass through the backing plate (5) and materialtarget (4) to form a magnetic field close to the surface of materialtarget. The balanced magnetic field arrangement (FIG. 1) can be achievedby mounting, to the device, a magnet assembly where the intensities ofindividual magnets have been adjusted to allow magnetic fluxes emanatingfrom N poles of the magnets to converge nearly totally onto S poles ofthe magnets, namely, a closed magnetic flux circuit to be formed betweenthe two poles.

Let's assume that the above device should be altered to provide anunbalanced distribution of magnetic fluxes. First, the magnet assembly(7) comprising magnets (6) as shown in FIG. 1 which has been set toproduce a balanced distribution of magnetic fluxes is removed, and it isexchanged for another magnet assembly (11) as shown in FIG. 2 where theintensities of individual magnets of the assembly have been adjusted soas to cause a part of magnetic fluxes emanating from N poles of themagnets not to return to S poles of the magnets but to be disperseddiffusely in a three-dimensional space (see URL:

http://www.kobelco.co.jp/p109/pvd/ubms.htm).

Alternately, switching the distribution of magnetic fluxes from thebalanced mode to the unbalanced one may occur as follows. A magnetassembly which has been set to give a balanced distribution of magneticfluxes is removed and disassembled. Into the magnet assembly thusdisassembled, a magnetic modifier (8) such as a ferromagnetic body maybe inserted as shown in FIG. 3 so as to modify the convergence state ofmagnetic fluxes to convert thereby the balanced mode of magnetic fluxdistribution into the unbalanced one.

However, the actual process necessary for the conversion is not sosimple. Let's assume that a device set to give a balanced distributionof magnetic fluxes as shown in FIG. 1 should be altered to give anunbalanced distribution as shown in FIGS. 2 and 3. Cooling water incontact with the backing plate (5) is purged; cooling water pipes (9)and a power cable (10) are removed; a balanced type magnet assembly (7)(bulky and heavy) is removed, and an unbalanced type magnet assembly(11) is mounted instead, or the balanced type assembly is modified byadding a modifier such as a ferromagnetic body thereto so as toestablish an unbalanced distribution of magnetic fluxes. In the lattercase, during the installment of the modified magnet assembly, thecooling water pipes (9) and power cable (10) must be reconnected. Allthese procedures are so complicated and require such a hard labor thatcompletion of them will take several hours.

Above all, adjustment of the magnet assembly to give a desiredconfiguration of magnetic field requires experience and technique sorich and high that even a technician skilled in the work does not feelease at the work. In addition, when modification of a magnet assemblyconsists of inserting a modifier constituted of a ferromagneticsubstance into a gap at one end of a magnet, insertion of the modifieritself is often difficult actually because there is not enough room atthe ends of a magnet. Thus, modification of a magnet assembly byinserting a modifier at one end of an appropriate magnet is ofteninfeasible.

In magnetron sputtering, the quality of a film formed thereby is veryimportant because it seriously affects all the subsequent processesleading to the production of a final product. In this respect, choice ofthe type of magnetic field design, and adjustment of a magnet assemblyin accordance with the design are very important. Thus, it is necessaryto separately use two kinds of cathodes operating on two differentmodes, one to give a magnetic field capable of evoking a balanceddistribution of magnetic fluxes and the other a magnetic field capableof evoking an unbalanced distribution of magnetic fluxes, depending onthe material of a film to be formed and purpose of the product.

Specifically, when the process for film formation may tolerate acomparatively high temperature, but must proceed at a high speed, acathode configured to give a balanced mode magnetic field should beadopted. On the contrary, when the process for film formation does nottolerate a high temperature, a cathode configured to give an unbalancedmode magnetic field should be used at a low temperature, even though thespeed with which film is formed will be reduced, because then it will bepossible to produce a film possessed of high quality crystals.

Requirement for switching from the balanced mode operation to theunbalanced one or vice versa occurs at a considerably high frequency inresearch and production sites, and thus the switching operationrequiring several hours as mentioned above has been a heavy burden forthose involved in the operation.

Even if it is decided, for example, to select a cathode arrangement thatgives an unbalanced magnetic field, it is still necessary to furtheradjust the radiation of magnetic fluxes into a three-dimensional space(by altering the intensities of individual magnets, their distribution,and size and shape of a ferromagnetic body) depending on the material ofa film to be formed so as to give an optimum result for that particularmaterial. In such an optimization work, it is often necessary to switchbetween the balanced mode operation and unbalanced one many times for asingle operation, which will further contribute to the prolongation oftime necessary for switching, and thereby add to the heavy burden.

Furthermore, adjusting the radiation of magnetic fluxes into athree-dimensional space (by altering the intensities of individualmagnets, their distribution, and size and shape of a ferromagnetic body)requires highly advanced technical knowledge and experience, and is noteasily achievable.

Still further, if it is required to convert configuration of the cathodefrom the balanced mode to the unbalanced one and the conversion isperformed by inserting a ferromagnetic body into a gap between a backingplate (5) and an appropriate magnet (6), a case is often encounteredwhere there is no enough room between the backing plate (5) and themagnet (6), because usually the cathode has been designed to allowmagnetic fluxes to efficiently converge onto the surface of a materialtarget. Because of this, even if it is required to alter theconfiguration of an existing magnetron sputtering device so as to give amagnetic field matching the property of a given material, adjustment ofthe radiation of magnetic fluxes into a three-dimensional space is oftenlimited within a certain range. Thus, it is often impossible to modifythe configuration of cathode to such a degree as to evoke a magneticfield that provides a desired unbalanced distribution of magneticfluxes. Particularly even if it is required to produce an unbalancedmagnetic field to enable low temperature sputtering, the requirement maynot be satisfied in some cases. Thus, demand is acute for a remedy todrastically solve the problem.

It has been known, to smoothly achieve low temperature sputtering, it ismore advantageous to employ a so-called dual magnetron sputtering deviceincorporating two units of magnetrons which allows the rapid formationof a film at a low temperature, as compared with an ordinary magnetronsputtering device based on a single unit of magnetron which will requirefull scale operation within its capacity to achieve the same purpose. Inthe dual magnetron sputtering device, the same problem as describedabove in relation to an ordinary magnetron sputtering device is alsoobserved: selection of the balanced type magnetic flux design orunbalanced one should be made according to the property of material, andswitching from one type to the other requires much labor and skill, andimposes a heavy burden to those involved in the operation. The problemalso remains to be solved.

Recently, demand is manifest for film forming sputtering which allowsthe formation of a film made of an inorganic material having a highmelting point over a substrate constituted of an organic polymer sheethaving a low melting point. To meet the demand, particularly to providesputtering allowing the formation of such a film at a low temperature,it is necessary to provide a device designed to give an unbalanceddistribution of magnetic fluxes, as well as a film formation methodenabling the formation of a film at a low temperature. It is oftendifficult to meet the demand even for a dual magnetron sputtering devicewhich has been designed to produce an unbalanced distribution ofmagnetic fluxes. Thus, it is often difficult even for a dual magnetronsputtering device to meet all the requirements imposed by the recentlydeveloped widely varied materials and their combinations. Solutions tothese problems are strongly wanted.

The background art relating to the first aspect of the invention hasbeen described above. Next, the prior art relating to the second aspectof the invention, that is, a dual magnetron sputtering device will bedescribed.

First, a conventional dual magnetron sputtering device will be describedwith reference to FIG. 9.

Referring to FIG. 9, two units of magnetrons (13) are placed opposite torespective material targets (14). Magnetic flux lines (15) are arrangedabreast crosswise to form a closed circuit emanating from N poles andending in S poles to take a balanced mode of magnetic flux distribution.In the device, two targets (14), (14) of the two units of magnetrons areplaced to be abreast on the same plane.

An alternate electric power having a desired waveform and frequency isapplied between the two units of magnetrons (13) to elicit sputtering.Then, a material constituting target (14) is turned into material vapor(17) which is released into the chamber of the device to deposit on asubstrate (16) to form a film there as intended, at a higher speed thanis possible with a single magnetron sputtering device.

However, with a conventional dual magnetron device, it is difficult toform a film with well-oriented crystals while keeping the target at alow temperature, or more typically not heating the target in any way,particularly when the material consists of an inorganic material havinga high melting point. For example, even if it was tried to prepare afilm of titanium oxide which has a photocatalytic activity on asubstrate kept unheated, the trial has never met success.

Therefore, it has been impossible to form, without heating, a film oftitanium oxide having a photocatalytic activity on a substrate made of amaterial having a low melting point represented by polyethyleneterephthalate which, on account of restrictions imposed by the physicalproperty of the material, requires non-heating film formation.

The merit of dual magnetron sputtering includes the rapid formation of afilm. However, if the formation of a film of titanium dioxide which willnormally have an excellent photolytic activity occurs on a glasssubstrate with heating at a deposition speed of 20 namometer or more perminute, the resulting film of titanium dioxide will not exhibit anexcellent photocatalytic activity characteristic with titanium dioxide.

To obtain a substrate coated with a film of titanium dioxide exhibitingan excellent photocatalytic activity characteristic with titaniumdioxide, it is necessary not only to select an appropriate material forthe substrate, but also to reduce the speed of film formation, whichspoils the merit inherent to dual magnetron sputtering.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

A first object of this invention is to simplify the designing of asputtering device that gives a desired configuration of magnetic fieldwhich has hitherto required much labor and ample experience, and toprovide a film formation method allowing the formation of an inorganicfilm coated material over a wide temperature range, utilizing amagnetron sputtering device in which the balanced mode and unbalancedone can be freely selected by switching.

A second object of this invention is to provide a dual magnetronsputtering device allowing the rapid formation of a film over a widetemperature range, and a film formation method allowing the rapidformation of an inorganic film coated material over a wide temperaturerange, utilizing a dual magnetron sputtering device as described above.

Means for Solving Problem

To attain the above objects, the present inventors studied hard andfound that the object related with the first aspect of the invention canbe readily achieved, when for example it is required to alter theoperation of a sputtering device from the balanced mode to unbalancedone, by placing a magnetic field adjusting member such as aferromagnetic body close to a target mounted on a backing plate (5).

Specifically, the inventors found it is possible to readily alter theoperation mode of a sputtering device. The balanced mode of operation istaken as a standard. Then, alteration of the operation from the balancedmode to unbalanced one can readily be achieved by attaching aferromagnetic body (8) close to a target (4) as shown in FIG. 4, andadjusting it or replacing an old ferromagnetic body with a new one.According to this method of altering the operation mode, the magneticfield design is essentially determined by the existing magnet assembly(7) in which magnets (6) have been arranged to produce a balanceddistribution of magnetic fluxes. Even when the operation is altered fromthe balanced mode to unbalanced one (or vice versa), it is not necessaryto separate a backing plate, cooling water pipes, and a power cable fromthe magnet assembly, modify them to match the unbalanced mode ofoperation, and reattach them to the device as with a conventionalmagnetron sputtering device.

The present inventors made a further finding. According to the methodbased on the finding, it is not necessary to carry out a specialoperation necessary for inserting a ferromagnetic body (8) into a gapbetween a magnet (6) and a backing plate (5) as shown in FIG. 3. Namely,the device can readily be altered to the unbalanced mode of operationwhile it maintains essentially the same configuration as in the balancedmode of operation.

The object related with the second aspect of the invention concerns adual magnetron sputtering device. In relation to this object, theinventors found that a highly active focus (19) of plasma is localizedin a comparatively narrow zone nearly at a middle point between twounits of magnetrons (13) (see FIG. 9).

Considering, by creating such a highly active focus of plasmadeliberately and making the most of it, it would be possible to manageto perform film formation under a stable condition, even when film isformed rapidly at a low temperature, the inventors continued theresearch.

As a result of this research effort, the inventors found that moreeffective activation of material vapor in plasma in a dual magnetronsputtering device can be achieved by rotating the planes sustaining twounits of magnetrons with respect to each other such that the two axesnormal to the planes intersect with each other at a certain appropriateangle, and that use of a mixture gas comprising two rare gases as asputtering gas contributes to the formation of an active focus of plasmawhich will promote the rapid formation of a film at a low temperature(FIGS. 10 and 13).

Certainly there are some among conventional dual magnetron sputteringdevices that are configured, being forced by some mechanicalrestrictions or other, to have two units of magnetrons (13) slantedtowards each other. However, this configuration has never been adoptedas a result of some idea or design concept which is derived fromrecognition: there is a highly active focus of plasma in a comparativelynarrow zone (equal in size to a cube having a side of severalcentimeters) at a middle point between two units of magnetrons (1); itis necessary to exactly determine the location of the focus (19); and itwill be advantageous to cause two main currents (18) of material vapordischarged from the two units of magnetrons with a certain angle betweenthem to flow through the active focus (19) of plasma. Thus, theconventional devices in question can never achieve the rapid formationof a film at a low temperature, because they have never been designed togive optimum condition and environment to attain the target hereconcerned.

To achieve the feature of the invention, only slanting two units ofmagnetrons (13) towards each other is not adequate. According to theinvention, it is necessary to select an optimum slanting angle, and forthis purpose it is necessary to exactly determine the location of theactive focus, and adjust the configuration of involved elements to allowtwo currents of material vapor to pass through the active focus toimpinge on a substrate. It should be understood that the basic designconcept of the inventive device is quite different from the designconcept of the apparently similar conventional devices as describedabove.

Of course, the optimum slanting angle may vary greatly depending oninvolved parameters of a given device, including the size and shape ofthe device, distance between a substrate (17) and a magnetron (13),distance between two units of magnetrons (13), etc. Thus, it isdifficult to determine an optimum slanting angle for a given deviceuniquely in terms, for example, of a certain distance parameter withinthe device. In practice, it is necessary to determine an optimumslanting angle individually for each device based on the above designconcept.

However, with the most commonly available dual magnetron sputteringdevices, the optimum slanting angle may fall within a range of 90°±45°.With specially configured dual magnetron sputtering devices, the anglein question may fall within a range of 90°±170 °.

The inventors further found that it is possible to expand the area of anactive focus (19) of plasma and raise the activity of the focus byslanting two units of magnetrons towards each other so that two currents(18) of material vapor radiated by the magnetrons (13) can merge witheach other on a substrate (17).

The angle between two units of magnetrons, distance between a substrate(17) and a magnetron (13), and distance between the two magnetrons (13)may vary from one device to another. However, generally an ordinarydevice configured according to the invention will have involved elementsarranged as shown in FIG. 13.

Referring to FIG. 13, the involved elements of a dual magnetronsputtering device are configured so that an angle formed between twolines one extending from the surface of material target (14) of onemagnetron (13) and the other extending from the surface of oppositetarget (14) of the other magnetron (13) falls within a range of 160 to20°, preferably 160 to 70°, and that an intersection region (23) where,for a pair of closely apposed erosion zones (21), one columnarprojection from the surface of erosion zone of one magnetron, whoseperiphery corresponds with that of said surface and whose direction isnormal to said surface, and the counterpart from the surface of erosionzone of the other magnetron cross with each other, can fall totally orpartially upon the surface (17) of a substrate where a film is to beformed, and allowing a film to be formed there.

An inventive dual magnetron sputtering device prepared based on thedesign concept as described above where two magnetrons are arranged tomeet the aforementioned requirements with respect to the location of atarget is not only effective for forming a film possessed of highquality crystals at a low temperature but is also compatible withcontinuous film formation by sputtering which is mandatory for massproduction.

Specifically, referring to FIG. 10 (or FIG. 13), it is readily possibleto continuously form films on a substrate by attaching, to a sputteringdevice, a conveyor mechanism for carrying a substrate horizontally (forexample, from the right to left of the figure).

The first requirement is the determination of an optimum angle betweentwo units of magnetrons as described above. The second requirement isbased on a further finding made by the inventors. They found it ispossible to effectively moderate the confinement of plasma to thesurface of a target (14) for one or both of two magnetrons (13), byaltering arrangement of the magnetron so as to allow it to generatemagnetic fluxes (20) having an unbalanced distribution.

When confinement of a plasma to the surface of a target is moderated,the plasma (not shown) tends to spread towards a substrate (17). As aresult, the active focus (19) of the plasma is also expanded, which maylead to the enhanced activation of material vapor in plasma. Thisprobably explains the reason why the rapid formation of a film at a lowtemperature becomes possible under this condition.

Care must be paid to the fact that an optimum result will be obtained ata certain degree of imbalance in the distribution of magnetic fluxes(the intensities of magnets should be adjusted such that not allmagnetic fluxes emanating from N poles return to S poles, but part ofthe fluxes is dispersed diffusely into a three-dimensional space). Inany case, setting up an unbalanced magnetic field will reduce thedensity of plasma close to the surface of a material target, whichreduces the speed with which a film is formed. Of course, reducing thespeed of film formation unduly will be disadvantageous. Thus, there isanother optimum point in terms of the speed of film formation for thedegree of magnetic flux imbalance.

It should be also taken into account that alteration of the magneticflux distribution may greatly increase the expanse of plasma, or reducethe area of active focus of plasma, or even annihilate the active focus.The optimum degree of imbalance in magnetic flux distribution is notlimited in a certain range, but should be determined individually foreach device. To obtain a device giving an unbalanced magnetic fluxdistribution, it is most preferred to utilize the procedures disclosedherein in relation to the first aspect of the invention.

The third requirement is the use of a gas mixture comprising two or morerare gases as a sputtering gas. Sputtering consists of impinging raregas particles onto a material target to release material vapor therefromas a result of the exchange of momentum. For this purpose, argon gas hasbeen used in an overwhelmingly majority of cases. The role of thesputtering gas is to effectively drive out material vapor from thesurface of a material target via the exchange of momentum, whileavoiding the entrapment by a forming film, and maintaining sputteringplasma.

To meet the requirement that the sputtering gas must avoid entrapment bya forming film, gases suitable for the sputtering gas are limited torare gases such as helium, neon, argon, krypton, xenon, and radon. It isnot a mere exaggeration to say that argon has been almost exclusivelyused as sputtering gas, because it is cheap, has an atomic weightcomparable to other elements used in association, and can efficientlydrive out material vapor via the exchange of momentum (see “GlowDischarge Processes,” p. 203, Chapman, John Willey & Sons, 1980).

As long as the sputtering gas is selected on the condition that it canefficiently vaporize a target material to maintain thereby plasma, thesputtering gas solely comprising argon will be adequate for allpurposes. Being based on such a point of view, no noteworthy study hasbeen made on a sputtering gas comprising a mixture of gases, its design,and interaction of those gases.

Contrary to this tendency, the present inventors have paid theirattention to the fact that the atom of a rare gas acting as a sputteringgas has a unique excitation level characteristic with the gas atom (forexample, argon gas comprises argon atoms having the same excitationlevel unique to the atom, and exchanges energies corresponding to thatenergy level with electrons and other particles in plasma). The overallactivity of a plasma including its focus is determined by the excitationlevels of particles involved in the plasma.

If a plasma is derived from a sputtering gas consisting solely of argongas, only the excitation level of argon atom exists in the plasma, andthe overall activity of the plasma is determined solely by theaforementioned excitation level of argon atom.

Let's assume an alternative case where a mixture gas comprising two ormore gases chosen from helium, neon, argon, krypton, xenon, and radon isused as a sputtering gas. Then, in a plasma derived from the sputteringgas, concomitantly generated are multiple excitation levels, forexample, of neon, argon, etc. Those excitation levels are naturallydifferent, and the overall behavior of the plasma including its activityis determined by those multiple excitation levels.

The present inventors confirmed use of a gas mixture comprising two ormore rare gases is more effective for the rapid formation of a film at alow temperature, as compared with the film formation performed in asputtering gas comprising a single rare gas. Use of a rare gas mixturemay also be effective for increasing the activity of plasma, that is,for further enhancing the activity of plasma focus (19) as shown in FIG.10.

The aforementioned mechanism, however, is not yet sufficiently clear atthe present state of knowledge, and awaits further studies. It isspeculated, however, that, when a rare gas mixture is used as asputtering gas, multiple excitation levels are generated in plasma whichwill more effectively increase the freedom of energy with whichparticles of plasma interact, and improves the efficiency of energyexchange among particles and leads to the enhanced activity of plasma,as compared with a case where a single rare gas is used as a sputteringgas.

The effect obtained from a sputtering gas comprising a gas mixture ismore conspicuous as the number of rare gases mixed becomes more, becausethen the freedom of energy becomes more enhanced. The mixture ratios ofindividual gases are not limited to any specific range, and can bevaried widely. However, a gas mixture comprising helium and neon, thatis, atoms having a comparatively small atomic weight where helium andneon account for 80% or more in volume should be avoided except for somespecial applications, because in such a sputtering gas the formation ofa film will be unduly retarded.

When a gas mixture comprising, for example, two rare gases is used as asputtering gas, and it is necessary to determine the optimum ratio oftwo gases, the most efficient method is to prepare as many rare gases aspossible, to take a combination of any two gases out of them in equalvolumes, to see the effect of the combined gas on film formation, and toincrease or decrease the flow amount of one or the other gas dependingon the result of film formation until an optimum condition for filmformation is obtained.

Use of a gas mixture as a sputtering gas also enhances the activity ofan active focus (7) of plasma.

Of the three requirements mentioned above, a dual magnetron sputteringdevice will have its film formation improved by only meeting the firstrequirement. However, it is more preferable for the device to meet acombination of any two out of the three requirements, or rather all thethree requirements as a whole than to meet any single one out of thethree requirements, because then the device will be able to exertexcellent effects, to allow a highly functional film to be rapidlyproduced at a low temperature.

The present invention has been achieved based on widely varied findings,and its features are roughly classified to two aspects of which one isdescribed in following paragraphs (1) to (8), and the other inparagraphs (9) to (19).

A first aspect of the invention: (1) a magnetron sputtering device inwhich a sputtering cathode is arranged to produce a balanceddistribution of magnetic fluxes and in which the balanced mode can beconverted into an unbalanced mode by placing an article that exhibitsferromagnetism at room temperature, onto or close to the surface of thesputtering cathode for holding a material target, and the unbalancedmode can be reconverted into the balanced mode by removing theferromagnetic article.

(2) The magnetron sputtering device as described in paragraph (1) inwhich the sputtering cathode is arranged to produce a balanceddistribution of magnetic fluxes and an element has been placed onto thesurface of the sputtering cathode for holding a material target, and inwhich the magnetic flux distribution can be converted from theunbalanced mode to the balanced one or vice versa, by replacing theelement with another element made of a material that exhibitsferromagnetism at room temperature.

(3) The magnetron sputtering device as described in paragraph (2) inwhich the element placed on the surface of the sputtering cathode forholding a material target is any one chosen from a middle pole, a middlepole cover, and an insulating body.

(4) The magnetron sputtering device as described in paragraph (3) inwhich the sputtering cathode arranged to produce a balanced distributionof magnetic fluxes is a square-shaped sputtering cathode.

(5) A film formation method for forming an well-crystallized film froman inorganic film formation material using a magnetron sputteringdevice, the method comprising selecting an unbalanced type magnetronsputtering device as described in any one of paragraphs (1) to (4),thereby enabling a film to be formed over a wide temperature range on asubstrate whose melting point falls between a low and high temperature.

(6) The film formation method as described in paragraph (5) for forminga well-crystallized film from an inorganic film formation material,wherein the substrate is an organic polymer sheet.

(7) The film formation method as described in paragraph (5) or (6) forforming a well-crystallized film from an inorganic film formationmaterial, wherein the inorganic film formation material is any one metalchosen from titanium, aluminum, zirconium, zinc, tin, indium, silicon,tantalum, bismuth, copper, boron, carbon, vanadium, manganese, tungsten,molybdenum, barium, strontium, yttorium, and niobium, and their oxides,nitrides, and borides.

(8) The film formation method as described in paragraph (7) for forminga well-crystallized film from an inorganic film formation material,wherein the oxide is titanium dioxide having a high photocatalyticactivity.

A second aspect of the invention: (9) A dual magnetron sputtering devicein which two magnetrons are slanted towards each other so that an angleformed between two lines one extending from the surface of a materialtarget of one magnetron and the other from the surface of a materialtarget of the other magnetron falls within a range of 160 to 20°,preferably 160 to 70°, to allow an active focus of plasma to convergeonto the surface of a substrate, thereby enabling the high speedformation of a film there at a low temperature.

(10) The dual magnetron sputtering device as described in paragraph (9)wherein the two magnetrons are set to produce an unbalanced distributionof magnetic fluxes.

(11) The dual magnetron sputtering device as described in paragraph (9)or (10) wherein gas to be introduced into the dual magnetron sputteringdevice comprises at least two gases chosen from helium, neon, argon,krypton, xenon, and radon.

(12) A film formation method for forming a film from an inorganic filmformation material using a dual magnetron sputtering device, the methodcomprising disposing the two magnetrons with respect to each other suchthat, when the surface of a target of each magnetron being taken as areference, an angle formed between the two reference lines one extendingfrom the surface of a target of one magnetron and the other from thesurface of a target of the other magnetron falls between 160 and 20°,and that an intersection region where, for a pair of closely apposederosion zones out of plural erosion zones developed on the two targets,one columnar projection from the surface of erosion zone of onemagnetron, whose periphery corresponds with that of said surface andwhose direction is normal to said surface, and the counterpart from thesurface of erosion zone of the other magnetron cross with each other,falls totally or partially upon the surface of a substrate where a filmis to be formed, and allowing a film to be formed on the substrate.

(13) The film formation method as described in paragraph (12) forforming a film from an inorganic film formation material using a dualmagnetron sputtering device wherein the dual magnetron sputtering devicehas been set to produce an unbalanced distribution of magnetic fluxes.

(14) The film formation method as described in paragraph (12) or (13)for forming a film from an inorganic film formation material wherein gasto be introduced into the dual magnetron sputtering device comprises atleast two chosen from helium, neon, argon, krypton, xenon, and radon.

(15) The film formation method as described in any one of paragraphs(12) to (14) for forming a film from an inorganic film formationmaterial wherein an organic polymer sheet is used as a substrate andfilm formation is performed at a low temperature.

(16) The film formation method as described in paragraph (15) forforming a film from an inorganic film formation material wherein theorganic polymer sheet is a polyethylene terephthalate polymer sheet.

(17) The film formation method as described in any one of paragraphs(12) to (14) for forming a film from an inorganic film formationmaterial wherein glass is used as a substrate, and a film formed on theglass.

(18) The film formation method as described in any one of paragraphs(12) to (17) for forming a film from an inorganic film formationmaterial wherein the inorganic film formation material is any oneinorganic material chosen from carbon, metals, oxides, nitrides,carbides, and borides.

(19) The film formation method as described in paragraph (18) forforming a film from an inorganic film formation material wherein theoxide is titanium dioxide having a high photocatalytic activity.

EFFECT OF THE INVENTION

According to the first aspect of the invention, it is possible toconvert the balanced type of magnetic field arrangement to theunbalanced one or vice versa by simply placing one or two or more easilyaccessible elements on a backing plate or on a target mounted to thebacking plate, or replacing an existing element(s) by one or two or moresuch elements. Thus, it is possible to dispense with the disassemblingand reassembling pipes and magnet assembly which are required for aconventional magnetron sputtering device each time the type of magneticfield arrangement must be altered, and to greatly reduce the timenecessary for conversion of the type of magnetic field arrangement.Thus, according to the first aspect of the invention, it is possible toreduce the time necessary for switching between the balanced andunbalanced types of magnetic field arrangement to as short as severalminutes, which will greatly improve the efficiency with which researchor production is advanced.

Particularly to provide an optimum magnetic field arrangement, it isnecessary to repeat an operation comprising a series of procedures suchas determination/adjustment of the intensities of individual magnets,adjustment of the position and size of a ferromagnetic body, and itsattachment. Thus, it is not a mere exaggeration to say that it would beessentially impossible to provide an optimum magnetic field arrangementwithin a period practically acceptable without the tactics provided bythe invention. In that respect, simplification of the work necessary forproviding an optimum magnetic field arrangement enabled by the inventionis particularly significant.

Conventionally, switching from the balanced type of magnetic fieldarrangement to the unbalanced one is achieved by inserting aferromagnetic body into a gap between a backing plate and a magnet, butthe gap is often too narrow to receive a required ferromagnetic bodywhich poses a problem. In contrast, according to the invention, such aferromagnetic body may be placed on a target or backing plate within awide vacuum chamber, instead of a narrow space between a backing plateand a magnet, and thus is free from the problem observed in aconventional device.

A dual magnetron sputtering device prepared according to the secondaspect of the invention wherein two magnetrons are simply disposed withrespect to each other such that an angle formed between two lines oneextending from the material holding surface of one magnetron and theother from the material holding surface of the other magnetron can fallwithin a specific range, wherein the atmosphere comprises a gas mixture,and wherein the cathodes are designed to produce an unbalanceddistribution of magnetic fluxes, allows a well-crystallized film to beformed rapidly at a low temperature over a plastic substrate withoutsuffering from the damage of crystals, as compared with a conventionaldual magnetron sputtering device where the two material holding surfacesof two magnetrons are disposed side by side on the same horizontalplane, because with the inventive dual magnetron sputtering device, anactive focus of plasma is expanded, and material vapor released from thematerial targets is broadly activated.

What is particularly noteworthy is that it is possible according to theinvention to form a film comprising polycrystal titanium dioxide havingan excellent photocatalytic activity on an unheated substrate, a featwhich has never been achieved by any known sputtering including dualmagnetron sputtering.

Another feature to be noted in relation to the invention is the speed offilm formation. Importantly, according to the method of the invention,the titanium dioxide film, despite that it has a thickness of 40 nmwhich is sufficiently thin to allow the rapid formation of film suitablefor mass production, still exhibits an effective photocatalyticactivity. The crystal structure of the thin film is of anatase typewhich is believed to exhibit a highest photocatalytic activity. Withregard to uniformly oriented crystals, the c-axis of crystal lattice isdisposed normal to the surface of substrate, indicating that the filmhas an excellent photocatalytic activity, in spite of its being formedunder an unheated condition. This feature represents the mostspectacular merit of the invention.

Still further, the invention provides a technique which for the firsttime enables the practical production of a compound product obtained bycoating the surface of a heat-labile sheet made, for example, of plasticsuch as polyethylene terephthalate (PET) with a film having aphotocatalytic activity, thereby conferring the sheet the propertiescharacteristic with a photocatalyst material such as defrosting, soilresistance, ultra-high hydrophilic activity, etc.

The effectiveness of the inventive technique has been proved only for asmall pilot device. However, since sputtering permits ready scaling-upas its notable characteristic feature, it will not be a mereexaggeration to say that the inventive method will open up, in themarket, a new gigantic field dealing with construction materialsincorporating “plastic materials having a photocatalytic activity.”

As stated above, the most remarkable feature of the invention is toallow the high speed formation of a film made of titanium dioxide havinga photocatalytic activity on an unheated substrate. However, theinventive method can also be applied as effectively for the formation ofa titanium dioxide film on a heated substrate. Thus, in this case too, afilm exhibiting an excellent crystallization as well as a highphotocatalyst activity will be obtained.

This feature is all the more notable because a conventional dualmagnetron sputtering device allows the rapid formation of a film havinga thickness of 20 nm only after heating a substrate to about 300° C.,and the resulting film having hardly any crystals exhibits only a weakphotocatalytic activity. In view of this, in place of currently marketedgoods called photocatalytic glass products which have been produced byheating substrate to several hundred degrees Centigrade, it will bepossible to provide, by using the inventive method and device, similarphotocatalystic glass products which are, however, by far excellent inperformance.

It has been stressed above and supported by the Examples given belowthat the inventive method is particularly effective for forming a thinfilm made of titanium oxide. Needless to say, however, the inventivemethod is effective for the formation not only of a film of titaniumoxide or like compounds, but also of a film of any compounds widelydiffered, as long as the compound allows the formation of a film bysputtering, particularly when it is required to form, at a lowtemperature, a film which exhibits excellent crystallization andmembrane performance. Specifically, the inventive method allows the highspeed and low temperature formation of a film of alpha alumina or othersimilar compounds which usually require, as an essential condition,heating as high as 1000° C. or more for film formation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the cathode of a conventional magnetronsputtering device which has been arranged to produce an balanceddistribution of magnetic fluxes.

FIG. 2 is a schematic diagram of the cathode of a conventional magnetronsputtering device in which the intensities and positions of individualmagnets are altered to produce an unbalanced distribution of magneticfluxes according to a conventional method.

FIG. 3 is a schematic diagram of the cathode of a conventional magnetronsputtering device in which conversion of a balanced magnetic fieldarrangement to an unbalanced one is achieved by inserting aferromagnetic body into a gap between a magnet and a backing plateaccording to a conventional method.

FIG. 4 is a schematic diagram of the cathode of an inventive magnetronsputtering device in which conversion of a balanced magnetic fieldarrangement to an unbalanced one is achieved by placing a ferromagneticbody on a surface of a backing plate to which a material target isattached.

FIG. 5 is a schematic diagram of the cathode of a magnetron sputteringdevice embodying the invention in which arrangement to produce abalanced magnetic field is achieved by placing a ferromagnetic body on asurface of a backing plate to which a material target is attached, as inthe sputtering device manufactured by Fraunhofer Institute, Germany.

FIG. 6 is a schematic diagram of the cathode of a magnetron sputteringdevice embodying the invention shown in FIG. 5 in which conversion of abalanced magnetic field arrangement to an unbalanced one is achieved byreplacing only a middle pole cover with another middle pole cover madeof iron (ferromagnetic at room temperature).

FIG. 7 shows an X-ray diffraction pattern of a titanium oxide filmformed via a sputtering cathode arranged to produce a balanced magneticfield as shown in FIG. 5.

FIG. 8 shows an X-ray diffraction pattern of a titanium oxide filmformed via a sputtering cathode arranged to produce an unbalancedmagnetic field as shown in FIG. 6.

FIG. 9 is a schematic diagram of a conventional dual magnetronsputtering device.

FIG. 10 is a schematic diagram of a dual magnetron sputtering device inwhich two magnetrons are disposed with respect to each other inaccordance with the invention.

FIG. 11 shows an X-ray diffraction pattern of a titanium oxide filmformed according to the invention on an unheated substrate consisting ofa polyethylene terephthalate resin sheet.

FIG. 12 is a photograph of a logo mark which is made visible on atitanium dioxide film by virtue of the photocatalytic activity of thefilm which has been formed by the inventive method on a polyethyleneterephthalate resin sheet kept unheated.

FIG. 13 is a diagram showing the positions of columnar projections fromerosion zones relative to a substrate in a dual magnetron sputteringdevice of the invention.

REFERENCE NUMERALS

(1) Middle pole cover

(2) Middle pole

(3) Insulating body

(4) Material target

(5) Backing plate

(6) Magnet

(7) Balanced type magnet assembly

(8) Ferromagnetic article

(9) Cooling water pipe

(10) Power cable

(11) Unbalanced type magnet assembly

(12) Ferromagnetic middle pole cover

(13) Dual magnetrons

(14) Dual material targets

(15) Balanced distribution of magnetic fluxes for dual magnetrons

(16) Shield for dual magnetrons

(17) Substrate

(18) Predominant current of material vapor

(19) Highly active focus

(20) Unbalanced distribution of magnetic fluxes for dual magnetrons

(21) Erosion zone

(22) Columnar projection from erosion zone in a direction normal to thelatter

(23) Intersection area formed between a pair of columnar projectionsmost closely apposed to each other.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention will be described below withreference to attached drawings and Examples. It should be understood,however, that the following description will be given for illustratingthe invention to be legible to readers, and not for limiting the scopeof the invention. Namely, modification of the embodiments including theconditions under which the embodiments are practiced will be possible,as long as the modification does not alter the spirit of the invention,and such modifications are naturally included within the scope of theinvention.

Embodiments Representing the First Aspect of the Invention

FIG. 4 is a schematic diagram of the cathode of an inventive magnetronsputtering device in which conversion of a balanced magnetic fieldarrangement to an unbalanced one is achieved by placing a ferromagneticbody on a surface of a backing plate to which a material target isattached.

FIG. 5 is a schematic diagram of the cathode of a magnetron sputteringdevice in which arrangement to produce a balanced magnetic field isachieved by placing a ferromagnetic body on a surface of a backing plateto which a material target is attached, as in the sputtering devicemanufactured by Fraunhofer Institute, Germany.

FIG. 6 is a schematic diagram of the cathode of an inventive magnetronsputtering device as shown in FIG. 5 in which conversion of a balancedmagnetic field arrangement to an unbalanced one is achieved by replacingonly a middle pole cover with another middle pole cover made of iron(ferromagnetic at room temperature).

Referring to FIG. 4, the cathode is constituted of a backing plate (5),magnets (6), and a magnet assembly (7) which are arranged in the samemanner as in a conventional magnetron sputtering device in which thecathode is arranged to produce a balanced magnetic field. Thus, anelement (8) made of a ferromagnetic material is mounted on the surfaceof backing plate (5) beside a material target. In FIG. 4, theferromagnetic element is mounted to backing plate (5) However, theferromagnetic element may be mounted onto the material target itself.

Among conventional magnetron sputtering devices, there are some that, inthe design of their cathode configuration, adopt the same design as thatobserved in the magnetron sputtering device manufactured by FraunhoferInstitute of Germany (FIG. 5). Namely, the cathode is designed tocomprise additional elements such as a middle pole cover (1), middlepole (2), and insulating body (3) arranged on a backing plate (5) besidea material target. Those magnetic sputtering devices have been acceptedas a powerful machine in the market. These additional elements (1), (2),and (3), however, are originally provided to inhibit aberrant dischargeswhich would otherwise occur during film formation, and have never beenprovided, according to the intention underlying the initial design, toutilize them as means to alter the configuration of magnetic field.

Namely, according to the initial design, the middle pole cover (1),middle pole (2) and insulating body (3) are all constituted of materialsthat do not exhibit ferromagnetism at room temperature. According to thepresent invention, any one or two chosen from these three elements orall the three elements are made of materials having a ferromagnetism atroom temperature, and their thickness and shape may also be modified asappropriate. It is also possible to place a ferromagnetic body inaddition to these elements to thereby alter the configuration ofmagnetic field so as to convert a balanced distribution of magneticfluxes into an unbalanced one.

If it is required to reconvert the unbalanced type of magnetic fieldarrangement now obtained into the balanced one, it is only necessary toreplace the ferromagnetic body with another body made of a material thatdoes not exhibit ferromagnetism at room temperature.

EXAMPLE 1

A magnetron sputtering device of this example in which the cathode hasbeen arranged to produce a balanced magnetic field uses, as its cathode,an RMS-200 type cathode designed/manufactured by Fraunhofer Institute,Germany.

The outline of the device is as shown in FIG. 5. In the cathode arrangedto produce a balanced magnetic field, the additional elements are amiddle pole cover (1) and middle pole (2) both of which are made ofstainless steel which does not exhibit ferromagnetism at roomtemperature, and a ferromagnetic body (3) constituted of a mica plate.To modify the cathode so as to produce an unbalanced magnetic field(FIG. 6) instead of the balanced magnetic field, in this particularexample, the middle pole cover (1) was replaced by another middle polecover made of a material which exhibits ferromagnetism at roomtemperature, specifically an iron-made middle pole cover (12). Themiddle pole cover (1) and ferromagnetic middle pole cover (12) had thesame size (about 10×3×0.5 cm), and had the same shape and thickness.

However, it is also possible to alter the intensity of an unbalancedmagnetic field by changing the shape and thickness of any additionalelement, thereby modifying the property of a resulting film.

In this particular example, the middle pole (2) and insulating body (3)used in the cathode arranged to produce a balanced magnetic field wereuse as they were. However, they may be replaced as appropriate byalternative elements made of ferromagnetic materials, and it is possibleby so doing to expand the range within which the property of a film canbe changed.

FIGS. 7 and 8 show X-ray diffraction patterns of titanium oxide filmsformed by RMS-200 type sputtering cathodes arranged to produce abalanced magnetic field and unbalanced magnetic field, respectively.

The two sputtering cathodes were identical except that the balance typecathode included a middle pole cover made of stainless steel while theunbalanced type cathode a middle pole cover made of iron. The conditionfor film formation was as follows: atmosphere, 0.5 Pa argon; flow ofoxygen, 7 cc/min; driving power, 3 kW, 50 kHz square pulses; and heatingof substrate, 300° C.

In a magnetron sputtering device in which the cathode is arranged toproduce a balanced magnetic field, the diffraction peak due to titaniumoxide is very weak in intensity, although it is observable. In contrast,in a magnetron sputtering device where the cathode is arranged toproduce an unbalanced magnetic field, the diffraction peak due totitanium oxide is strong and marked, which clearly indicates thecharacteristic feature of an unbalanced type magnetron sputtering devicewhich allows the formation of a well crystallized film at a lowtemperature. This serves as a powerful evidence for demonstrating theeffectiveness of the present invention, and confirms the well-controlledswitching of magnetic field arrangement from the balanced type to theunbalanced one and vice versa in an magnetron device prepared accordingto the invention.

Switching of magnetic field arrangement from the balanced type to theunbalanced one or vice versa is achieved according to the invention byremoving easily accessible several screws (not shown) which are attachedto the surface of a backing plate, and then replacing an existing middlecover (1) with another appropriate middle cover, and completes in a fewminutes, in contrast with a conventional device in which alteration ofthe magnetic field arrangement requires the removal/reconnection ofwater pipes (9), power cable (10), magnets (6), and magnet assembly (7)which will take a far longer time.

By using a magnetron sputtering device in which the cathode is arrangedaccording to the invention, it is possible to obtain a well-crystallizedfilm not only from titanium oxide but also from metals as describedbelow, and their oxides and nitrides. The metals include titanium,aluminum, zirconium, zinc, tin, indium, silicon, tantalum, bismuth,copper, boron, carbon, vanadium, manganese, tungsten, molybdenum,barium, strontium, yttorium, and niobium, and their oxides and nitrides.The device prepared according to the invention is confirmed to beeffective in the satisfactory formation of a film of any one materialchosen from the above list. The inventive method, however, can beapplied to any other molecule than those cited above, and application ofthe inventive method to a given molecule can be rejected for nojustifiable reason.

Embodiments Representing the Second Aspect of the Invention

Next, embodiments representing the second aspect of the invention willbe described with reference to attached drawings and Examples. It shouldbe understood, however, that those embodiments will be given only forillustrating the invention, and that the scope of the invention will notbe limited in any way by those examples.

EXAMPLE 2

The dual magnetron sputtering device basically used in this exampleconsists of an MLC-200 type dual magnetron sputtering deviceincorporating two units of RMS-200 type magnetrons designed/manufacturedby Fraunhofer Institute, Germany.

As shown in FIG. 10, the two units of magnetrons (13) are slantedtowards each other so that an angle is equal to 90° which is formedbetween the two lines one extending from the surface of material targetof one magnetron and the other from the counterpart surface of the othermagnetron, which enables two main currents of the material (17) from therespective magnetrons (13) can merge at a place on or close to thesurface of a substrate (16). The distance between the center of thesubstrate and the center of each material target is 20 cm.

To convert, for the two units of magnetrons (13), a balanceddistribution of magnetic fluxes into an unbalanced one (19), for eachunit of magnetron, a non-magnetic middle pole cover (not shown) inherentto the RM-200 type magnetron (13) was replaced by an iron-made middlepole cover that exhibits ferromagnetism at room temperature and has thesame size with that of the genuine middle pole cover: two ferromagneticmiddle pole covers were set to the sites where the two genuine middlepole covers had been set in the RM-200 type magnetrons (13), in place ofthe latter.

Optimization of the convergence degree of magnetic fluxes (19) can beachieved readily and accurately as is known in the prior art by changingthe size and shape of middle poles and other elements adjacent to them,or the materials constituting them, as has been described above inrelation to the first aspect of the invention.

Since the details of the procedures taken for adjustment have been givenabove in relation to the first aspect of the invention, they will beomitted here.

What is noteworthy here is that the sputtering gas used for the dualmagnetron sputtering device consists of a gas mixture. Specifically, thegas mixture was obtained by mixing three gas flows consisting of argon,krypton, and helium to give a gas mixture comprising the three gases ata 2:1:1 flow ratio. The gas mixture was introduced at 80 cc/min inoverall flow into the device to give a pressure of about 0.5 Pa in thechamber of the device.

In each of the magnetrons (13), titanium metal was set as a materialtarget (14). A 3 kW pulsed output was delivered at 50 kHz to eachmagnetron electrode (13) to evoke a sputtering plasma (not shown) closeto the material target constituted of titanium metal, to sputter metalatoms.

Introduction of the gas mixture was adjusted to generate an overall flowof about 7 cc/min close to the surface of material target on each of themagnetrons (13). The substrate (16) consists of a sheet made of apolyethylene terephthalate resin having a thickness of 188 μm. Anuncoated surface of the sheet comprising only pure polyethyleneterephthalate was employed for a coating surface. The substrate was keptunheated, and thus a heater (not shown) set to heat the substrate waskept out of action.

Under the aforementioned condition, film formation was performed for 20minutes. Then, a titanium oxide film having a thickness of about 800 nmwas obtained. The film formation speed in this case was as high as 40nm/min.

An X-ray diffraction pattern obtained from the film is shown in FIG. 3.The pattern shows a strong diffraction curve indicating that crystalshave a clear TiO₂ anatase structure. In addition, the pattern emphasizessome diffraction curves with certain indices, which indicates that theTiO₂ anatase film exhibits excellent crystallization, and the c-axis ofcrystal lattice is disposed normal to the surface of substrate.

It has never been possible to obtain a film exhibiting such clearcrystallization as this by using a dual magnetron sputtering deviceaccording to a conventional method, even when the film is formed on aglass substrate heated to 300° C. Also it has never been possible toobtain a titanium oxide film having a detectable photocatalytic activityby using a dual magnetron sputtering device according to a conventionalmethod, even when the film is formed on a glass substrate heated to 300°C. It has been possible to obtain a titanium oxide film having a barelydetectable photocatalystic activity only after an additional heatingtreatment consisting of heating to about 500° C. is introduced afterfilm formation.

In contrast, a film with TiO₂ crystals having an anataze orientationformed on a polyethylene terephthalate substrate according to theinventive method exhibits a strong photocatalytic activity immediatelyafter the non-heating film formation, and can eliminate the need foradditional heating treatment. FIG. 4 shows the results ofphotocatalystic activity measurement performed on a film with TiO₂crystals having an anataze orientation formed on a polyethyleneterephthalate substrate according to the inventive method. Themeasurement was performed immediately after the non-heating filmformation without any intervention of additional heating treatment.

A photo mask having a pattern representing a certain logo mark (NIMS)printed thereon was applied to the surface of a film with TiO₂ crystalshaving an anataze orientation, and the assembly was immersed in a 0.1mol/L aqueous solution of silver nitrate, and exposed for 5 minutes toUV containing light guided via an optical fiber from a light sourceconsisting of a 200 W xenon lamp.

Areas exposed to UV light had blackish silver films formed thereon as aresult of photocatalytic activity of the film, while the remaining areasshielded against UV light had thereon the intact film with TiO₂ crystalshaving an anataze orientation, thus making the negative image of thelogo mark clearly visible.

A comparable titanium oxide film was obtained by using a dual magnetronsputtering device according to a conventional method: the film wasformed on an unheated substrate (5) and received no additional heatingtreatment. The film was submitted to the same measurement as describedabove, but did not show any photocatalytic activity.

As described above, it becomes possible according to the invention toform a photocatalytic film with TiO₂ crystals having an anataseorientation on an unheated substrate, a feat that has never beenachieved by any conventional methods. A film obtained as described aboveaccording to the invention exhibits a higher photocatalytic activitythan a comparable film obtained by a conventional method under heatingto about 300° C. Namely, it is possible according to the invention toobtain a high performance film exhibiting a higher photocatalyticactivity than does a comparable film obtained by a conventional method,even though film formation occurs according to the invention at a lowtemperature (under non-heating condition) which has been believed to bedisadvantageous for the production of a film exhibiting well-formedcrystallization and high performance.

INDUSTRIAL APPLICABILITY

It is expected that film formation technique will add to its importanceas one of basic techniques in the future.

According to the first aspect of the invention, it is possible toreadily switch, for a given magnetron sputtering device, the magneticfield arrangement from the balanced type to the unbalanced type or viceversa, and the switching operation can be performed rapidly andaccurately. For a conventional magnetron sputtering device, theswitching operation is so complicated that even those who have deeptechnical knowledge and skill have to spend considerable time and laborfor the operation. In contrast, according to the method of theinvention, it is possible even for a person having an ordinary skill inthe field to readily alter the mode of magnetic field arrangement in ashort period. The thus improved operability of a magnetron sputteringdevice according to the invention involved in the formation of film isimportant in view of the expectation that film formation technique willadd to its importance in the future, and will greatly contribute to theprogress of industry.

The second aspect of the invention relates to a dual magnetronsputtering device, and a dual magnetron sputtering device in whichrelevant elements are arranged in accordance with the invention willallow high speed film formation to occur at a low temperature. Such adual magnetron sputtering device, because of its being highlyadvantageous, will be widely accepted, and greatly contribute to theprogress of industry.

Particularly, as described above in relation to Examples, according tothe invention it is possible to form a film with titanium dioxidepolycrystals exhibiting an excellent orientation and high photocatalyticactivity on an unheated substrate, a feat that has never been achievedby any conventional methods. The technique itself is so valuable as tobe notable, and will be vigorously utilized in the future.

What is noteworthy further still is the speed of film formation. Namely,according to the method of the invention, a titanium dioxide film formedat a rate of 40 nm/min, which is sufficiently high to allow massproduction, still exhibits an effective photocatalytic activity, whichis profoundly important. The crystals of a titanium dioxide film formedaccording to the invention have an anatase type crystal structure thatis known to have the highest photocatalytic activity of all the crystalstructures permitted to titanium dioxide materials, and furthermore thecrystals are uniformly oriented to allow the c-axis of crystal latticeto be disposed normal to the surface of substrate. This observation wellexplains the reason why the film exhibits an excellent photocatalyticactivity, in spite of its being formed under non-heating condition.

The invention provides a technique which enables the practicalproduction of a compound product obtained by covering the surface of aheat-labile sheet made, for example, of plastic such as polyethyleneterephthalate (PET) with a film having a photocatalytic activity,thereby conferring, as desired, the film the properties characteristicwith a photocatalyst material such as defrosting, soil resistance,ultra-high hydrophilic activity, etc. The technique will be widelyaccepted and products produced based on the technique will form a bigshare in the market.

1. A magnetron sputtering device in which a sputtering cathode isarranged to produce a balanced distribution of magnetic fluxes and inwhich the balanced mode can be converted into the unbalanced mode byplacing an article that exhibits ferromagnetism at room temperature,onto or close to the surface of the sputtering cathode for holding amaterial target, and the unbalanced mode can be reconverted into thebalanced mode by removing the ferromagnetic article.
 2. The magnetronsputtering device as described in claim 1 in which the sputteringcathode is arranged to produce a balanced distribution of magneticfluxes and an element has been placed onto the surface of the sputteringcathode for holding a material target, and in which the magnetic fluxdistribution can be converted from the unbalanced mode to the balancedone or vice versa, by replacing the element with another element made ofa material that exhibits ferromagnetism at room temperature.
 3. Themagnetron sputtering device as described in claim 2 in which the elementplaced on the surface of the sputtering cathode for holding a materialtarget is any one chosen from a middle pole, a middle pole cover, and aninsulating body.
 4. The magnetron sputtering device as described inclaim 3 in which the sputtering cathode arranged to produce a balanceddistribution of magnetic fluxes is a square-shaped sputtering cathode.5. A film formation method for forming a well-crystallized film from aninorganic film formation material using a magnetron sputtering device,the method comprising selecting an unbalanced type magnetron sputteringdevice as described in claim 1, thereby enabling a film to be formedover a wide temperature range on a substrate whose melting point fallsbetween a low and high temperature.
 6. The film formation method asdescribed in claim 5 for forming a well-crystallized film from aninorganic film formation material, wherein the substrate is an organicpolymer sheet.
 7. The film formation method as described in claim 5 forforming a well-crystallized film from an inorganic film formationmaterial, wherein the inorganic film formation material is any one metalchosen from titanium, aluminum, zirconium, zinc, tin, indium, silicon,tantalum, bismuth, copper, boron, carbon, vanadium, manganese, tungsten,molybdenum, barium, strontium, yttorium, and niobium, and their oxides,nitrides, and borides.
 8. The film formation method as described inclaim 7 for forming a well-crystallized film from an inorganic filmformation material, wherein the oxide is titanium dioxide having a highphotocatalytic activity.
 9. A dual magnetron sputtering device in whichtwo magnetrons are slanted towards each other so that an angle formedbetween two lines one extending from the surface of a material target ofone magnetron and the other from the surface of a material target of theother magnetron falls within a range of 160 to 20°, preferably 160 to70°, to allow an active focus of plasma to converge onto the surface ofa substrate, thereby enabling the high speed formation of a film thereat a low temperature.
 10. The dual magnetron sputtering device asdescribed in claim 9 wherein the two magnetrons are set to produce anunbalanced distribution of magnetic fluxes.
 11. The dual magnetronsputtering device as described in claim 9 wherein gas to be introducedinto the dual magnetron sputtering device comprises at least two chosenfrom helium, neon, argon, krypton, xenon, and radon.
 12. A filmformation method for forming a film from an inorganic film formationmaterial using a dual magnetron sputtering device, the method comprisingdisposing the two magnetrons with respect to each other such that, whenthe surface of a target of each magnetron being taken as a reference, anangle formed between the two reference lines one extending from thesurface of a target of one magnetron and the other from the surface of atarget of the other magnetron falls between 160 and 20°, and that anintersection region where, for a pair of closely apposed erosion zonesout of plural erosion zones developed on the two targets, one columnarprojection from the surface of erosion zone of one magnetron, whoseperiphery corresponds with said surface and whose direction is normal tosaid surface, and the counterpart from the surface of erosion zone ofthe other magnetron cross with each other, falls totally or partiallyupon the surface of a substrate where a film is to be formed, andallowing a film to be formed on the substrate.
 13. The film formationmethod as described in claim 12 for forming a film from an inorganicfilm formation material using a dual magnetron sputtering device whereinthe dual magnetron sputtering device has been set to produce anunbalanced distribution of magnetic fluxes.
 14. The film formationmethod as described in claim 12 for forming a film from an inorganicfilm formation material wherein gas to be introduced into the dualmagnetron sputtering device comprises at least two chosen from helium,neon, argon, krypton, xenon, and radon.
 15. The film formation method asdescribed in claim 12 for forming a film from an inorganic filmformation material wherein an organic polymer sheet is used as asubstrate and film formation is performed at a low temperature.
 16. Thefilm formation method as described in claim 15 for forming a film froman inorganic film formation material wherein the organic polymer sheetis a polyethylene terephthalate polymer sheet.
 17. The film formationmethod as described in claim 12 for forming a film from an inorganicfilm formation material wherein glass is used as a substrate, and a filmformed on the glass.
 18. The film formation method as described in claim12 for forming a film from an inorganic film formation material whereinthe inorganic film formation material is any one inorganic materialchosen from carbon, metals, oxides, nitrides, carbides, and borides. 19.The film formation method as described in claim 18 for forming a filmfrom an inorganic film formation material wherein the oxide is titaniumdioxide having a high photocatalytic activity.